(1) Field of the Invention
The present invention relates generally to finishing fabric and, more particularly, to an automatic fabric width control system for a fabric compactor.
(2) Description of the Prior Art
In the manufacture of apparel, particularly t-shirts and the like, after the greige goods have been knit they are inspected and transferred to a finishing line. During finishing, the goods are bleached or dyed in preparation for cutting. Since "soft" materials, such as fabric, are not dimensionally stable and may vary from source to source, it is the general practice to run the fabric through a compactor to set the fabric before cutting.
Generally speaking, a compactor includes a mechanical spreader for spreading the fabric to a preset width and at least one pair of steam heated rolls for setting the fabric to that width. If there was little variability in finished fabric, all that would be necessary would be to set the width of the mechanical spreader and run a trial length of fabric web, make a measurement of the width of the compacted fabric and readjust the width of the mechanical spreader. However, fabric varies considerably from machine to machine based on knit type, counts per inch and other variables including variables introduced into the fabric web during finishing. Accordingly, it is necessary to constantly monitor the width of the fabric exiting the compactor. Unfortunately, it is difficult for a human operator to make adjustments on width of fabric exiting a compactor at about 80 yards a minute.
In the past, PID open loop controllers have been used to control the width between the mechanical separator bars based on the measured width of the fabric exiting the compactor. However, prior art systems using a PID open loop controller measured the width of the fabric directly and then made an adjustment in the width of the spreaders. While this seems simple enough, because of the speed that the cloth is exiting the compactor there often is no relationship between the width of the measured cloth exiting the compactor and the cloth entering the mechanical spreader on the inlet of the compactor. Accordingly, this would often cause the control system to oscillate out of control as the control system tried to correct errors that were no longer the cause of the problem.
This has become more of a problem as fabric speed has increased for more modern equipment. In addition, by the time the fabric has been finished and compacted, there is a substantial investment in the fabric which is wasted if the fabric web cannot be held to the proper dimensions for the style of the garment which is being cut from it.
Thus, there remains a need for a new and improved fabric width control system which is sufficiently sensitive to measure small changes in a high speed fabric web while, at the same time, overcomes the tendency of such a control system to go into an oscillation mode.